I did it once, long ago when I needed to fit inside a curved rocker base, so the resulting radius that it needed to cut was quite generous.
I decided to sacrifice an old metal Stanley that I'd bought new in the '60s, that never worked well (probably because my sharpening skills in those days weren't up to getting it right). The mouth is rather wide on this shave.
Anyway, I found out that the curved profile needs to be straight across, gradual in shape, but still enough meat left to support the blade so that it doesn't dig in...... and that was the problem.
After a fair bit of experimenting I got the shape right enough but then found out the 'Golden Rule of Monkeying-Around With Spoke-shaves'. That is to keep a flat registration area, about 1/8 inch or so wide surrounding the mouth. Begin the curves from these points onward.
Do I still use curved spokes now? As a last resort, I may once in a blue-moon, but my go-to implement now final shaping of for flat curves such as rocker sections is a Stanley 82 scraper with an aggressive burr on the blade. It is controllable..... fast...... cuts......gets into curves both inside and out.....
Sadly, they're very rare in the UK - not marketed here for some reason - but a brilliant bit of kit. I think that Veritas make something similar, but a little smaller.
But, to sum up, I found that a small, flat area around the mouth section is essential to support the blade tip in an approach that allows cutting to take place instead of the dreaded dig-in. Resist the temptation to curve the whole sole in one sweep.
Good luck
